Concealed space conditions can be configured, as provided in NFPA 13 (2007) Chapter 8, Section 8.6, including Table 8.6.2.2.1(a) and FIGURE 8.6.4.1.4, which is incorporated by reference in its entirety, as an attic beneath a roof or ceiling with the combustible concealed space being of wood joist or wood truss construction with truss members three feet or less on center and a slope or pitch of 4 in 12 (rise over run) or greater. NFPA-13 (2007) Section 11.2.3.2.4, which is incorporated by reference in its entirety, provides that for sloped ceilings, the area of sprinkler operation (design area) shall be increased by 30% without revising the density for sprinklers used on sloped ceilings with a pitch exceeding 1 in 6 in non-storage applications. The density requirement of a concealed space system can be determined under the light hazard density/area curve of FIGURE 11.2.3.1.1 of NFPA-13 (2007) which is incorporated by reference in its entirety. Currently under NFPA-13 (2007) at Table 8.6.2.2.1(a), which is incorporated by reference in its entirety, the minimum pressure for a concealed space sprinkler system is 20 pounds per square inch (psi).
NFPA-13 Section 11.2.3.2.5 provides that for a dry system, the sprinkler operation area be increased by 30% over the wet system design requirements without revising the density. Thus, known dry combustible concealed space fire protection systems beneath a sloped ceiling or roof are subject to a 30% penalty for the dry system and the additional 30% penalty for sloped ceiling requirements.